American Forest Association_Details for Wood Frame Construction

55 Pages·1.524 MB·English

DETAILS FOR
CONVENTIONAL WOOD
FRAME CONSTRUCTION
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American
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Copyright © 2001
American Forest & Paper Association
WOOD CONSTRUCTION DATA 1 1
TABLE OF CONTENTS
Chapter/Title Page Chapter/Title Page
Introduction .............................................3 Firestopping ............................................8
General Scope.........................................3 Draftstopping..........................................8
Grade Marking ........................................3 Exterior Wall Framing...........................8
Lumber Seasoning .................................4 Interior Partition Framing....................9
TYPES OF FRAME CONSTRUCTION Framing Around Chimneys and
Fireplaces..........................................9
Platform Frame.......................................4
Roof and Ceiling Framing................. 10
Balloon Frame .........................................5
Insulation and Vapor Retarders....... 11
Fastenings...............................................5
Exterior Siding and Coverings ........ 11
Plank and Beam Construction ............5
Flooring ................................................. 12
Truss-Framed Construction.................5
Wood Decks ......................................... 13
Foundations.............................................5
Conclusion ............................................ 14
Protection Against Termites and
Decay ..................................................6 Appendix.................................................52
Floor Framing.......................................... 7
LIST OF TABLES
Table Page
I. Nominal and Minimum-Dressed Sizes of
Boards, Dimension and Timbers..............15
II. Wood Shingle and Shake Weather
Exposures ................................................. 16
AMERICAN FOREST & PAPER ASSOCIATION
2 DETAILS FOR CONVENTIONAL WOOD FRAME CONSTRUCTION
LIST OF ILLUSTRATIONS
Figure Page Figure Page
1. Platform Frame Construction......................17 35. Second Floor Overhang of Exterior Wall,
Joists at Right Angles to Supporting
2. Balloon Frame Construction .......................18
Walls...............................................................33
3. Methods of Loading Nails............................18
36. Second Floor Overhang of Exterior Wall,
4. Sizes of Common Wire Nails .......................19
Joists Parallel to Supporting Walls.............33
5. Masonry Foundation Wall and Footing ......20
37. Firestopping Around Pipes..........................34
6a. Permanent Wood Foundation - Crawl
38. Firestopping of Dropped Ceilings...............34
space..............................................................20
39a.Firestoppingof Masonry Walls - Floor........35
6b. Permanent Wood Foundation -
39b.Firestopping of Masonry Walls - Ceiling ....35
Basement.......................................................21
40. Draftstopping of Trussed Floors.................36
7a. Sump for Poorly Drained Soils....................22
41. Multiple Studs at Corners............................36
7b. Sump for Medium to Well Drained Soils ....22
42. Wall Framing at Intersecting Partitions......36
8. Pier Foundation and Anchorage.................23
43. Exterior Wall Openings, Header Details
9. Clearance Between Earth and Floor
with Cripple Studs ........................................37
Framing..........................................................23
44. Exterior Wall Openings, Header Details
10. Support for Basement Post.........................23
with Joist Hangers........................................37
11. Floor Framing at Exterior Wall ....................24
45. Framing of Bay Window...............................38
12. Girder Framing in Exterior Wall...................24
46. Wall Framing at Gable Ends ........................38
13. Termite Shields..............................................24
47a.Wall and Floor Framing at Fireplace...........39
14. Anchorage of Sill to Foundation Wall.........25
47b.Hearth Centering Detail................................39
15. Nailing Built-up Beams and Girders...........25
48a.Clearance of Fireplace Trim.........................40
16. Joist End Bearing .........................................25
48b.Section Through Mantle...............................40
17. Joist Supported on Ledger..........................26
49. Building Paper and Siding Application......41
18. Joist Supported by Metal Framing
50. Application of Wood Shingles.....................41
Anchors..........................................................26
51. Roof Framing Ceiling Joists Parallel to
19. Joists Resting on Girder..............................26
Rafters............................................................42
20. Joists Resting on Steel Beam .....................26
52. Roof Framing, Ceiling Joists
21. Diagonal Bridging of Floor Joists...............27
Perpendicular to Rafters..............................42
22. Solid Bridging of Floor Joists .....................27
53. Roof Framing Gable Overhang....................43
23. Framing of Tail Joists on Ledger Strip.......28
54. Flat Roof Framing.........................................43
24. Framing of Tail Joists by Framing
55. Valley Rafter Roof Framing..........................44
Anchors..........................................................28
56. Hip Rafter Roof Framing..............................44
25. Framing of Header to Trimmer by Joist
57. Roof Framing at Eave...................................44
Hangers..........................................................28
58. Shed Dormer Roof Framing.........................45
26. Notching and Boring of Joists....................28
59. Gable Dormer Framing.................................46
27. Framing Over Bearing Partition,
Platform Construction..................................29 60. Roof Framing Around Chimney ..................46
28. Framing Over Bearing Partition, Balloon 61. Roof Ventilation Requirements ...................47
Construction..................................................29 62. Ventilating Eave Overhangs ........................47
29. Framing Under Non-Bearing Partition........30 63. Wood Siding Patterns and Nailing..............48
30. Attachment of Non-Bearing Partition to 64. Corner Treatments for Wood Siding...........48
Ceiling Framing.............................................30 65. Application of Masonry Veneer to Wood
31. Interior Stairway Framing ............................31 Framing..........................................................49
32. Stairway With a Landing ..............................32 66. Wood Strip Flooring .....................................49
33. Framing Supporting Bathtub.......................32 67. Wood Deck.....................................................50
34. Second Floor Framing, Exterior Wall .........33 68. Ceiling-Floor Partition Separation..............51
AMERICAN WOOD COUNCIL
WOOD CONSTRUCTION DATA 1 3
DETAILS FOR CONVENTIONAL WOOD FRAME CONSTRUCTION
INTRODUCTION The first approach to achieving a strong, durable struc-
ture, involving economical use of materials, is to follow a
Wood frame construction is the predominant method basic modular plan for layout and attachment of framing
of building homes and apartments in the United States, members. Such methods use a 4-foot design module,
enabling this nation to have the world’s best housed popu- which governs a 16-inch spacing of joists, studs, rafters
lation. and panel sheathing products. This module also provides
Increasingly, wood framing is also being used in com- for alternate 24-inch spacing of floor, wall and roof fram-
mercial and industrial buildings. Wood frame buildings are ing where floor and roof trusses are used, and
economical to build, heat and cool, and provide maximum accommodates 24-inch spacing of studs where wind loads
comfort to occupants. Wood construction is readily adapt- permit, or where larger studs are required for thicker in-
able to traditional, contemporary and the most futuristic sulation or heavier floor and roof loads.
building styles. Its architectural possibilities are limitless.
History has demonstrated the inherent strength and Terminology
durability of wood frame buildings. The purpose of this Previous versions of this document have followed the
document is to summarize and illustrate conventional con- practice of using “shall” and “should” to emphasize those
struction rules as a guide for builders, carpentry foremen, mandatory instructions covering fire and life safety as
building inspectors and students in the building trades. separate from general good practices cover durability, re-
The application of conventional construction rules may duced maintenance costs and best performance of
be limited by building code requirements in use where products. Recognizing that the term “should,” in practice,
the building is being constructed. Conventional construc- can be considered as optional and that failure to follow
tion provisions, as found in this publication, represent such provisions can result in serious damage or excessive
techniques with a history of satisfactory performance. maintenance costs to the home owner, this publication
Today, some building codes may require a more rigor- states the procedure as it is to be illustrated in the house
ous structural design methodology than is associated with plan, followed by the job foreman and subcontractors, and
conventional construction. This requirement may result from enforced by the building inspector.
a need for better building performance when the structure is Wherever possible, the provisions described are in-
exposed to moderate-to-high wind, seismic, and snow loads. tended to conform to current code provisions; however, it
AF&PA publishes the Wood Frame Construction Manual is recommended that the local building code be checked
for One- and Two-Family Dwellings (Appendix, Item 1) to for additional requirements. Other methods of building
provide solutions based on engineering analysis, in accor- may provide equal, or possibly, improved performance.
dance with recognized national codes and standards. Like These, however, must provide performance assurance ac-
conventional construction, the engineered solutions are pro- ceptable to the owner and the building inspector.
vided in a prescriptive format.
Dimensioning
GENERAL SCOPE In general, dimensions for framing lumber, wood sid-
ing and trim referenced in this document are nominal
With any building material or product, sound construc- dimensions; i.e., 2x4, 2x6, etc., for simplicity. Actual sur-
tion and installation practices must be followed to assure faced dimensions conform with those in Product Standard
durability and trouble-free performance. Areas for PS 20, published by the American Lumber Standards Com-
economy in basic design and house construction are cov- mittee (Appendix, Item 2). A summary of these
ered in numerous publications. However, skimping on dimensions is set forth in Table I.
materials or using poor building practices in constructing
the house frame saves little. Such practices may reduce GRADE MARKING
the strength and rigidity of the structure and cause diffi-
culty in attachment of cladding materials and trim. Framing lumber, also referred to as “dimension” lum-
Therefore, the details in this document are not intended to ber, must be properly grade marked to be acceptable under
be bare minimums; rather, they reflect requirements for the major building codes. Such grade marks identify the
producing sound, low maintenance wood frame buildings. grade, species or species group, seasoning condition at
AMERICAN FOREST & PAPER ASSOCIATION
4 DETAILS FOR CONVENTIONAL WOOD FRAME CONSTRUCTION
time of manufacture, producing mill number and the grad- Final moisture content of lumber in the building varies
ing rules writing agency. with the geographic region and with location in the struc-
The bending strength, F , and the stiffness or modulus ture. Floor joists over a crawl space may reach seasonal
b
of elasticity, E, may be determined from the grade mark for moisture contents in excess of 14 percent. Roof trusses and
lumber used as joists, rafters, and decking. These values rafters, on the other hand, may dry below 6 percent. Squeak-
enable determination of allowable spans for the lumber. ing floors and loose nails in wallboard or siding can be
Grading rules for various softwood and certain hard- reduced by allowing framing to season to a moisture con-
wood species are written by regional rules writing tent which is as close as possible to moisture levels it will
agencies, which operate within the system, established by reach in service and by utilizing modern framing techniques
the American Lumber Standards Committee (ALSC) un- and products, including glued-nailed floor systems, grooved
der the authority of the U.S. Department of Commerce. or ring-shanked nails, and drywall screws.
This system provides for on-going inspection of lumber
produced to the applicable rules and for monitoring of the Protection of Materials
inspection agencies by the Board of Review of the ALSC. Lumber, panel products and millwork (windows, doors
Engineering values and tables of allowable spans for and trim) should be protected from the weather when de-
framing lumber are available from the American Forest livered at the building site. Preparation of a construction
& Paper Association (Appendix, Items 3 and 4), and the schedule will assure that lumber and millwork are deliv-
regional rules writing agencies. ered as needed. Follow these simple rules:
(1) Support framing lumber, plywood and panel prod-
LUMBER SEASONING
ucts at least six inches above ground and protect
them below and above with a waterproof cover such
Wood loses moisture from the time it is cut and manu-
as plastic film. Finish lumber and flooring, particu-
factured into lumber until it reaches equilibrium in service.
larly, are to be protected from ground or concrete
Best performance of wood frame buildings is obtained when
slab moisture and kept under cover – preferably in-
the moisture content of framing lumber at the time the build-
doors – until installation.
ing is enclosed with sheathing and interior finish, is as close
as possible to the condition it will reach in service. (2) Store door and window assemblies, siding and ex-
Grading rules which conform with American Soft- terior trim inside. Where this is not practical, these
wood Lumber Standard, PS 20, provide for framing lumber materials are to be elevated from the ground and
surfaced to standard sizes at the unseasoned condition (S- protected above and below with a weatherproof
Grn), at 19 percent maximum moisture content (S-Dry) cover.
and at 15 percent maximum moisture content (KD) or
Millwork items are often pre-treated with a water-
(MC-15). Standard sizes apply to S-Dry (19% max), with
repellent preservative as received. Whether treated
slightly larger sizes provided for S-Grn so that both prod-
or not, such materials are to be stored under cover.
ucts reach approximately the same size after seasoning in
Untreated exterior millwork should receive a wa-
service. MC-15 lumber is produced to the same standard
ter-repellent preservative treatment before
size as S-Dry. In some cases engineering stress values as-
installation.
signed to lumber produced to different seasoning
conditions are adjusted to reflect the effects of seasoning. (3) Store interior doors, trim, flooring and cabinetwork
Lumber should be protected from weather at the job in the building. Where wet plaster is used it must be
site. Buildings should be roofed and enclosed with sheath- permitted to dry before interior woodwork, cabinetry
ing without delay to maintain the original dryness of the and flooring are installed.
lumber or to help unseasoned lumber reach equilibrium
during construction.
TYPES OF FRAME CONSTRUCTION
PLATFORM FRAME erected. This is the type of construction most generally
used in home building, Figure 1.
In platform-frame construction, first floor joists are Platform construction is easy to erect. It provides a
completely covered with sub-flooring to form a platform work surface at each floor level and is readily adapted to
upon which exterior walls and interior partitions are various methods of prefabrication. In platform systems it
AMERICAN WOOD COUNCIL
WOOD CONSTRUCTION DATA 1 5
is common practice to assemble wall framing on the floor exterior sidings. Details for this method of framing are pro-
and tilt the entire unit into place. vided in Plank and Beam Framing for Residential Buildings
- Wood Construction Data No. 4, published by the Ameri-
BALLOON FRAME can Forest & Paper Association (Appendix, Item 5).
In balloon-frame construction, exterior wall studs con- TRUSS-FRAMED CONSTRUCTION
tinue through the first and second stories. First floor joists and
exterior wall studs both bear on the anchored sill, Figure 2. The strength and resilience of wood construction is
Second-floor joists bear on a minimum 1x4-inch ribbon strip, due to its framework of structural lumber combined with
which has been let-in to the inside edges of exterior wall studs. a covering of subflooring, wall and roof sheathing. Addi-
In two-story buildings with brick or stone veneer exte- tional engineering of the system through use of floor and
riors, balloon framing reduces variations in settlement of roof trusses and metal framing anchors provides even
framing and the masonry veneer. Where exterior walls are greater rigidity and permits wider spacing of floor and
of solid masonry, balloon framing of interior bearing parti- roof supporting members.
tions also reduces distortions in door and closet openings
in crosswalls. The requirement for longer studs, and the FOUNDATIONS
difficulty in accommodating current erection practices and
firestopping, has reduced the popularity of this system. A firm foundation, consisting of properly installed
footings of adequate size to support the structure, is es-
FASTENINGS sential to the satisfactory performance of all buildings.
Such foundations fully utilize the strength and resilience
Nails, used alone or in combination with metal fram- of wood frame construction.
ing anchors and construction adhesives, are the most Footings should extend below exterior grade suffi-
common method of fastening 1- and 2-inch framing lum- ciently to be free of frost action during winter months. Where
ber and sheathing panels, Figure 4. Ring or spiral shank roots of trees are removed during excavation or when build-
nails provide higher load-carrying capacities than com- ing on filled ground, the ground should be well compacted
mon nails of the same diameter, and are particularly useful before footings are installed or concrete is poured.
where greater withdrawal resistance is required. Where poor soil conditions exist, satisfactory foun-
Nailed joints provide best performance where the load dations may be constructed of treated timber piles capped
acts at right angles to the nails. Nailed joints with the load with wood or concrete sills. Footing requirements are cov-
applied parallel to the nail (in withdrawal) should be ered in the local building code. It is good practice,
avoided wherever possible, since joints are weakest when generally, to make the footing thickness equal to the thick-
nailed in this manner, Figure 3. ness of the foundation wall and the footing projection equal
Where tilt-up wall framing is not practical, or where to one-half the foundation wall thickness.
stronger stud-to-plate attachment is required (as in the use Two principal foundation types are commonly used.
of rigid foam sheathing), toe-nailing is the most practical These are concrete and pressure preservative treated wood.
method of framing studs and plates. Concrete footings with poured concrete or masonry block
In toe-nailing, nails are driven at a 30-degree angle foundation walls are most common. An increasingly popu-
(approximately) to the stud. Studs can be pre-drilled to lar foundation for houses and other wood frame buildings
simplify this operation and prevent excessive splitting. is the “Permanent Wood Foundation” which is accepted
by all model building codes and the Department of Hous-
PLANK AND BEAM CONSTRUCTION ing and Urban Development (HUD).
In the plank and beam framing method, beams of ad- Concrete Foundations
equate size to support floor and roof loads are spaced up Concrete footings are frequently unreinforced. Where
to eight feet apart. Floors and roofs are covered with 2- unstable soil conditions exist, however, reinforced con-
inch planks. These serve as subflooring and roof sheathing, crete is used. This requires engineering analysis of the
and, where tongue-and-grooved planking is used, provide footing. The foundation wall may be of poured concrete
an attractive finished floor and ceiling. or masonry blocks. Masonry block basement walls typi-
Ends of floor and roof beams are supported on posts cally have a ½-inch coat of Portland cement mortar applied
which provide the wall framing. Supplementary framing to the exterior. When set, the mortar parging is covered
between posts permits attachment of wall sheathing and with two coats of asphalt to resist penetration of the wall
AMERICAN FOREST & PAPER ASSOCIATION
6 DETAILS FOR CONVENTIONAL WOOD FRAME CONSTRUCTION
by ground water, Figure 5. Masonry block walls are tures for Permanence-Wood Construction Data No. 6
capped at the top with 4 inches of solid masonry or con- (Appendix, Item 8). The following practices are basic:
crete. Drain tiles are installed around the entire footing All roots and scraps of lumber are removed from the
perimeter of concrete foundations. These lead to a storm immediate vicinity of the house before backfilling.
drain or sump with pump to a positive drain. Loose backfill is carefully tamped to reduce settle-
ment around the foundation perimeter. Grading at the
Wood Foundations foundation and over the building site is sloped to provide
Permanent wood foundations are engineered systems drainage away from the structure.
consisting of wood framing and plywood sheathing that
have been pressure treated with heavy concentrations of Unexcavated Spaces
preservative to assure freedom from decay and insect at- Exposed ground in crawl spaces and under porches or
tack. The system is used with both basement and crawl decks is covered with 6-mil polyethylene film. Minimum
space foundations, Figures 6a and 6b. clearance between the ground and the bottom edge of beams
Permanent wood foundations are particularly suitable or girders is at least twelve inches. Clearance between the
for cold weather construction where the entire foundation bottom of wood joists or a structural plank floor and the
system can be prefabricated. The footing and basement ground is a minimum of 18 inches, Figure 9. Where it is
area consists of a layer of gravel or crushed stone of 4- not possible to maintain these clearances, approved1 pres-
inch minimum thickness. Treated wood footing plates of sure treated or naturally durable wood species are used.
adequate thickness and width are placed on the stone base
at the wall perimeter. These support foundation stud walls Columns and Posts
of treated lumber framing and plywood sheathing which Posts or columns in basements and cellars, or exposed
have been designed to support vertical and lateral loads. to the weather, are supported by concrete piers or pedestals
Exterior plywood joints are caulked and basement foun- projecting at least 1 inch above concrete floors or decks
dation walls are covered with 6-mil polyethylene film to and 6 inches above exposed earth. Wood posts and col-
direct ground water to the gravel base. Basement floors umns are separated from concrete piers by an impervious
are concrete slab or wood flooring laid on treated wood moisture barrier, except when approved pressure treated or
joists on sleepers. A 6-mil polyethylene film is placed over naturally durable wood species are used, Figures 9 and 10.
the gravel base beneath the slab or wood floor. Wood posts or columns which are closer than 8 inches
Drain tiles are not required with permanent wood foun- to exposed ground in crawl spaces or supporting porches
dations. Ground water at the wall perimeter drains through or decks are of approved pressure treated or naturally du-
the gravel footing and the gravel slab base to a sump which rable wood species.
leads to a daylight outlet or is pumped to a storm drain,
Figure 7. Such basements have a superior record for main- Exterior walls
taining dry interior conditions. Additional information on Wood framing and sheathing used in exterior walls
Permanent Wood Foundations is available from AF&PA and are installed at least 8 inches above exposed earth (in-
the Southern Pine Council (Appendix, Items 6 and 7). cluding finished grade), unless approved pressure treated
or naturally durable wood species are used, Figures 11
Other Foundations and 12.
Other foundation types include free standing piers,
piers with curtain walls, or piers supporting grade beams. Beams and Girders in Masonry Walls
Piers and their footings must be of adequate size to carry Openings or cavities in masonry walls to support the
the weight of the house, contents and occupants. Pier spac- ends of beams, girders, or floor joists are of sufficient size to
ing will depend upon arrangement of floor framing and provide a minimum of ½-inch clearance at the top, sides and
location of bearing walls and partitions. Spacing in the ends of such members, unless pressure preservative treated
range of 8 to 12 feet is common practice, Figure 8. or naturally durable wood species are used, Figure 12.
PROTECTION AGAINST TERMITES AND Wood Supports Embedded in Ground
DECAY Wood supports embedded in the ground to support
permanent structures shall be treated with approved pres-
Good construction practice prevents conditions that sure preservative treatments. Wood posts, poles and
could lead to decay or termite attack. Details for termite columns which support permanent structures and which
and decay prevention are found in Design of Wood Struc-
1 Approved, as used in this text, means approved by the authority having jurisdiction.
AMERICAN WOOD COUNCIL
WOOD CONSTRUCTION DATA 1 7
are embedded in concrete in direct contact with earth or approximately 6-foot intervals. Bolts are embedded at least
exposed to the weather, shall be treated with approved 6 inches in poured concrete walls and at least 15 inches in
pressure preservative treatments. masonry block walls, Figure 14. Metal anchor straps,
embedded in foundation walls at sufficient intervals to
Siding permit adequate nail fastening to sills, may also be used.
A minimum clearance of 6 inches is maintained be-
tween the finished grade and the bottom edge of all types Sills on Piers
of siding used with wood frame buildings. Such clear- Sills supported by free-standing piers must be of ad-
ance permits ready inspection for termite activity and equate size to carry all imposed loads between piers. They
improved performance of exterior paint and stain finishes. may be of solid wood or of built-up construction such as
described for beams and girders. Sills are anchored to piers
Crawl Space Ventilation with ½-inch bolts embedded at least 6 inches in poured
Crawl spaces are vented by openings in foundation concrete and at least 15 inches in masonry block, Figure 8.
walls. The number and size of such vent openings are de-
termined to provide a minimum total vent area equal to Beams and Girders
1/150 of the crawl space ground area. For example, a 1500 Beams and girders are of solid timber or built-up con-
sq. ft. ground area would require a total of 10 sq. ft. of struction in which multiple pieces of nominal 2-inch thick
vented opening, or 10 vents, each 1 square foot in net lumber are nailed together with the wide faces vertical.
opening size. Corrosion resistant mesh with ¼-inch maxi- Such pieces are nailed with two rows of 20d nails-one
mum openings is recommended. row near the top edge and the other near the bottom edge.
A 6-mil plastic film ground cover in the crawl space Nails in each row are spaced 32 inches apart. End joints
reduces the required amount of ventilation to 10 percent of the nailed lumber should occur over the supporting
of the preceding recommendation. With ground cover column or pier. End joints in adjacent pieces should be at
protection, vents may have operable louvers. Vent open- least 16 inches apart, Figure 15. Glued-laminated mem-
ings should be placed to provide cross ventilation and bers are also used. Beams and girders that are not
occur within 3 feet of corners. continuous are tied together across supports. Bearing of
at least 4 inches is required at supports.
Termite Control
After removal of all scrap wood from the building Selection and Placing of Joists
perimeter, treatment of the soil around the foundation with Span Tables for Joists and Rafters (Appendix, Item 4)
an approved termiticide is the most effective protection published by the American Forest & Paper Association,
against subterranean termites. Properly installed termite provides maximum allowable spans for the different spe-
shields also provide protection where the interiors of foun- cies and grades of lumber depending upon floor and roof
dation walls are not easily inspected, Figure 13. design loads and spacing of the members.
Joist end-bearing should not be less than 1½ inches
Additional Requirements on wood or metal and 3 inches on masonry. Joists are usu-
In geographical areas where experience has demon- ally attached to sills by two toe-nails, or by metal framing
strated a need for more protective measures, the anchors, Figures 8, 11 and 16. Joists should be placed so
requirements of the preceding paragraphs may be modi- the top edge provides an even plane for the sub-floor and
fied to the extent required by local conditions. finished floor. It is preferable to frame joists into the sides
of girders to reduce the cumulative effect of seasoning
FLOOR FRAMING shrinkage, Figures 17, 18, 19 and 20.
Floor framing consists of a system of sills, girders, Bridging
joists or floor trusses and sub-flooring that provides sup- Adequately nailed subflooring will maintain the up-
port for floor loads and gives lateral support to exterior per edges of floor joists in proper alignment. Nailing the
walls. ends of joists to band joists or headers, Figures 11 and
24, provides additional joist support that, under normal
Sills on Foundation Walls conditions, eliminates the need for intermediate bridging.
Sills resting on continuous masonry foundation walls Where the nominal depth-to-thickness ratio of joists ex-
are generally of nominal 2x4 or 2x6 lumber. They are an- ceeds 6, or where builders have encountered problems
chored to masonry walls with ½-inch bolts at with twisting of joists in service, intermediate joist bridg-
AMERICAN FOREST & PAPER ASSOCIATION
8 DETAILS FOR CONVENTIONAL WOOD FRAME CONSTRUCTION
ing is installed at 8-foot intervals. Bridging may also be FIRESTOPPING
accomplished with cross braces of nominal 1x4-inch lum-
ber or solid 2-inch lumber, Figures 21 and 22. All concealed spaces in wood framing are firestopped
with wood blocking or other approved materials. Block-
Framing of Floor Openings ing must be accurately fitted to fill the opening and to
Headers, trimmers and tail joists form the framing for prevent drafts between spaces, Figures 2, 16, 27, 28, 31,
floor openings. Trimmers and headers are doubled when and 32.
the header span exceeds 4 feet. Headers more than 6 feet Openings around vents, pipes, ducts, chimneys, fire-
in length are supported at the ends by joist hangers or places and similar fixtures which would allow passage of
framing anchors unless they are bearing on a partition, fire are filled with non-combustible material, Figure 37.
beam or wall. Tail joists which exceed 12 feet in length Other firestopping requires 2-inch lumber or two
are supported on framing anchors or on ledger strips not thicknesses of 1-inch lumber with staggered joints, or one
less than nominal 2x2 inches, Figures 23, 24 and 25. thickness of ¾-inch plywood with joints backed by 1-inch
lumber or ¾-inch plywood.
Notching and Boring of Joists Sills and plates normally provide adequate
Notches or holes in joists for plumbing or wiring shall firestopping in walls and partitions. However, stopping is
not be cut in the middle one-third of the joist span. Notches required at all intersections between vertical and horizon-
in the outer-third sections of the span may be no greater tal spaces such as occur at soffits, dropped ceilings and
than one-sixth the joist depth. Where notches are made at coved ceilings, Figure 38.
the joist ends for ledger support, they may be no greater Furred spaces on masonry walls are firestopped at each
than one-fourth the joist depth. Holes in the outer-third floor level and at the ceiling level by wood blocking or by
joist sections are limited in diameter to one-third the joist non-combustible material of sufficient thickness to fill the
depth and are cut with the edge of the hole no closer than space, Figure 39.
2 inches to the top or bottom edges, Figure 26.
DRAFTSTOPPING
Support of Partitions
Bearing partitions are normally placed over girders In single family residences, draftstopping is required
or walls which support the floor system. Where floor fram- parallel to main framing members in floor/ceiling assem-
ing is adequate to support the added load, bearing partitions blies separating usable spaces into two or more
may be offset from supporting members by no more than approximately equal areas with no area greater than 500
the joist depth, unless floor joists are designed to carry square feet. Materials for draftstopping may be 3/8-inch
the increased load, Figures 27 and 28. plywood or ½-inch gypsum board, Figure 40.
Where non-bearing partitions run parallel to floor
joists, the joist under the partition is doubled to support EXTERIOR WALL FRAMING
increased loads which frequently occur adjacent to the
partition, Figures 29 and 30. Exterior wall framing must be of adequate size and
strength to support floor and roof loads. Walls must also
Overhang of Floors resist lateral wind loads and, in some locations, earthquake
Where second-floor joists project over the first story forces. Top plates are doubled and lapped at corners and
wall at right angles, they are cantilevered to support the at bearing partition intersections to tie the building into a
second story wall, Figure 35. Where the overhanging wall strong structural unit. A single top plate may be used where
is parallel to the second floor joists, a double joist sup- roof rafters or trusses bear directly above wall studs. In
ports lookout joists which extend at right angles over the such cases adequate corner ties are required, particularly
first story wall, Figure 36. The double joist is located where non-structural sheathing is used.
inside the supporting wall at a distance equal to twice the
overhang. Lookout joists are framed into the double joist Stud Size and Spacing
by framing anchors or a ledger strip nailed at the upper Studs in exterior walls of one and two-story buildings
edge. are at least nominal 2x4 inches with the 4-inch dimension
forming the basic wall thickness. Stud spacing is normally
16 inches in exterior walls, although 24-inch spacing of
2x4 studs is acceptable in one-story buildings if wall
sheathing or siding is of adequate thickness to bridge
AMERICAN WOOD COUNCIL